The present invention is directed to a sensing device comprising a sensing element such as an optical fiber with a means or device for measuring the alterations or changes in specific physical parameters of a light which has been coupled into the fiber and passed therethrough to determine specific physical influences applied to the fiber.
A sensing device of the type which measures a physical influence by determining alterations or changes in a specific physical parameters of a light passing through an optical fiber are known. An example of such a sensing device is a ring interfermeter, which is employed for example for the purpose of sensing rotational speeds. In the case of ring interferometers of this type, light is coupled into both ends of the fiber. The light, which passes through the fiber in one direction, and the light which passes through the fiber in the opposite direction are then brought into interference through superimposition and in this state are measured by an intensity meter. Thus, the intensity of the light, which is passed through the fiber, is measured as a physical parameter. The physical effect on the fiber is the rotational movement of the fiber and the measured intensity will vary with the angular velocity of this rotational movement. The dependency of the intensity upon the angular velocity is based on the Sagnac effect.
Other physical effects or influences on a fiber can alter specific parameters of the light which is passed through the fibers. Examples are pressure, tension, and also temperature influences on the fiber, which can for example, alter the traversal speed of the light through the fiber or also its polarization state as a physical parameter. A sensing device which has an optical fiber as the sensing element, and includes means for coupling light into the fiber and means for measuring alterations in specific physical parameters of the light passing through the fiber to determine special physical influences applied to the fiber have already been proposed and described in my copending U.S. application Ser. No. 179,665, filed Aug. 19, 1980, which application was based on German patent application No. P 29 36 303.9. This device would react to either temperature, tension or temperature variations. In particular, a sensing device of this type can be employed as an accoustical sensor.
As a specific parameter, parameters or indications of the traversed light are to be understood which are actually measured by a measuring device. A parameter of this type need not be a direct parameter but on the contrary it can also be dependent parameter. In the case of the above indicated example of a ring interferometer, the direct parameter would be the transit time of the light which is passed through the fiber. In the case of a rotating fiber, the Sagnac effect, namely does not bring about reciprocal transit time differences between light which passes through the fiber in both directions. This transit time difference in turn brings about indirect intensity changes in the interference light. In this sense the intensity is a dependent parameter.